A series of direct-connected tests were conducted on a rotating detonation ramjet with a cylindrical isolator-combustor configuration, under the conditions of a total temperature of 860 K and Ma=2 inflow. The influence of the combustor leading edge expansion angle(θ=30°,45°,60°, 90°) on the propagation characteristics, operating range, and pressure distribution of detonation waves was investigated. The results indicate that the combustion mode is consistently deflagration when the expansion angle of the leading edge of the combustor is 90°. As the expansion angle gradually decreases, the combustion mode transitions towards sawtooth and hybrid mode (including single wave stage). When the expansion angle of the leading edge of the combustor is 30°, the rotating detonation exhibits the widest self-sustaining operating range and highest combustor pressure. Additionally, as the expansion angle decreases, the lower limit of the equivalence ratio for achieving the hybrid mode decreases. At the same time, the impact of combustion modes on the inflow was analyzed and it was found that the periodic high-frequency pressure oscillation in the sawtooth wave/hybrid mode combustor could cause the positioning of leading edge of the shock train in the isolator to move upstream. The hybrid mode has the most significant impact on supersonic inflow.